The present disclosure relates to viewers that are equipped with multifocal lenses each having a plurality of focal lengths to be selected and are capable of adjusting focal lengths in accordance with distances of gazing points, i.e., points of fixation, of users.
To cope with abnormalities, such as myopia and presbyopia, in the accommodation ability, viewers having the function of automatically adjusting focal lengths, such as glasses and goggles using convex and concave lenses, have been proposed. Since we have a wide range of gazing point distance in daily live and a fixed focus lens has a narrow range of focal point, the use of multifocal lenses has been promoted for such a viewer. To adjust the focal length of a multifocal lens, it is necessary to know the gazing point (point of fixation) of the user.
Japanese Unexamined Patent Publication No. H04-273211 describes a technique of detecting a change in electro-oculogram occurring with eye movement in order to obtain a gazing point and adjusting the focal length of a varifocal lens in accordance with the gazing point.
Japanese Unexamined Patent Publication No. 2010-262189 proposes a technique of switching a focal length by automatic determination of a gazing point distance based on, for example, movement of a user in a viewer that switches among predetermined focal lengths.